<?php
$num1=$_GET["num1"];
$num2=$_GET["num2"];
$op=$_GET["op"];
switch($op){
    case'+':$result=$num1+$num2;break;
    case'-':$result=$num1+$num2;break;
    case'*':$result=$num1+$num2;break;
    case'%':$result=$num1+$num2;break;
}
?>

<html>
<body>
<form action="cal.php" method="get">
<input type="text" name="num1" value="<?php echo $num1?>"/>
<select name="op">
    <option value="+"<php echo $op='+'?'selected':''>>+</option>
    <option value="-"<php echo $op='-'?'selected':''>>-</option>
    <option value="*"<php echo $op='*'?'selected':''> >*</option>
    <option value="%"<php echo $op='%'?'selected':''>>%</option>
</select>
<input type="text"  name="num2" value="<?php echo $num2?>"/>
=
<input type="text" name="result"/>
<button type="submit">计算</button>
</form>
</body>
</html>
